A. Field of the Invention
This invention relates to thermal regeneration systems for anti-pollution purposes and in particular to apparatus and a method for reducing the flow of unpurified industrial or commercial effluent into the atmosphere.
B. Prior Art
Thermal regeneration apparatus is known such as shown in the U.S. Pat. No. 3,895,918 issued to James H. Mueller on July 22, 1975. In that system, a number of heat-exchange sections are arranged about and in communication with a central, high temperature chamber. Each heat-exchange section includes a heat-exchange bed with a large number of refractory elements or "stones" confined within a heat-exchange bed by inward and outward perforated retaining walls. An industrial effluent to be purified is applied to an inlet duct ring which has branch ducts that distribute the effluent to selected ones of the heat-exchange sections whenever its associated inlet valve is open. In such a case, the effluent traverses the heat-exchange bed which has a temperature gradient from the front inner retaining wall to the rear outer retaining wall. The front inner wall and region are hotter than the regions located more toward the outside since the front is closer to the very high temperature central combustion or incineration chamber.
All of the heat-exchange sections are also coupled by branch conduits to an exhaust duct ring, the ring itself being connected to an exhaust fan that draws the gaseous contents of the exhaust ring out and applies them to an exhaust stack or equivalent.
The effluent initially traverses a first heat-exchange bed in one of the inlet heat exchange sections after passing through an open inlet valve (the outlet valve of that section being kept closed) and then is drawn through the central combustion chamber where it is purified by high temperature oxidation. It is then drawn through at least a second heat-exchange bed to whose stones the purified combustion products lose their very high heat. In the second heat exchange section, the inlet valve remains closed whereas the outlet valve is open.
When the next cycle begins, however, a second heat-exchange section may be caused to operate as an inlet heat exchanger, whereas the first inlet heat-exchange section may have its role reversed to function as an outlet heat exchanger. Thus, in the next cycle, the first heat exchange section will have its outlet valve turned off and its inlet valve opened whereas the second inlet heat exchange section will have just the opposite valve condition. Before the next cycle begins, however, there is an intermediate period in which both valves of the first section will be turned off so that any residual effluent in that section may be drawn off by the suction generated by the exhaust fan. Otherwise, when the next cycle begins and the condition of the valves in the first section are reversed, this residual unpurified effluent might be drawn directly into the outlet exhaust ring without having traversed the heat-exchange bed in the first section, the central combustion chamber and the heat-exchange bed in the second heat-exchange section. This would result in the emission of noxious or dangerous gases into the atmosphere.
The valves used at the inlet and outlet of the respective heat-exchange sections are often metal-to-metal because of the temperatures involved. Even if the valves are nominally closed, imperfections in manufacture of the valves or defects in them induced by heat or by other operating causes may result in leaks of the effluent through the inlet and outlet valves, especially when there is a changeover of a heat-exchange section from an inlet to an outlet mode so that the effluent flows directly in the outlet exhaust ring thereby bypassing the thermal oxidation process.
Although there is a problem with valves such as these insofar as leakage is concerned, there is no practical way to measure such leakage once it has been installed in the apparatus as shown. While an individual valve can have its leakage measured on a test stand using ambient air, the latter is so much lower than actual operating gas temperatures that such tests are not too valid. To simulate actual operating temperatures would require elaborate heat exchange equipment and other expensive equipment. Furthermore, because of shop machining practices and allowable tolerances, no two valves which are supposed to be the same have the same leakage rate. While it may be that the leakage is less than 1%, even that small amount may be intolerable in certain areas where antipollution measures are stringently enforced.
Several ways of combating this leakage have been proposed among which is a plan whereby double valves in series are used at the inlet and outlet valves so as to reduce the pressure differential across each valve and thereby the rate and volume of leakage. This proposal is made in the co-pending application Ser. No. 052,670, filed June 27, 1979 entitled "Double Valve Anti-Leak System for Thermal Regeneration Incinerators." This method may be further improved, as explained in that application, by applying some of the purified exhaust gas under pressure to the space between each pair of series valves. While this is an effective method to prevent leakage, it does require the use of a double number of valves and appurtenant controls.
It is therefore among the objects of the present invention to:
(1) provide a system for preventing leakage of effluent across valves in incineration systems.
(2) provide an anti-leak system for incineration apparatus which does not require the use of double valves and the concomitant instrumentation for them.